In the electronics industry, as products such as cell phones, camcorders and digital media players become smaller and smaller, increased miniaturization of integrated circuit (IC) or chip packages has become more and more critical. At the same time, higher performance and lower cost have become essential for new products.
In response to the demands for newer packaging, many innovative package designs have been conceived and brought to market. The multi-chip module has achieved a prominent role in reducing the board space used by modern electronics. However, multi-chip modules, whether vertically or horizontally arranged, can also present problems because they usually must be assembled before the component chips and chip connections can be tested. That is, because the electrical bond pads on a die are so small, it is difficult to test die before assembly onto a substrate. Thus, when die are mounted and connected individually, the die and connections can be tested individually, and only known-good-die (“KGD”) that is free of defects is then assembled into larger circuits. A fabrication process that uses KGD is therefore more reliable and less prone to assembly defects introduced due to bad die. With conventional multi-chip modules, however, the die cannot be individually identified as KGD before final assembly, leading to KGD inefficiencies and assembly process yield problems.
A multi-chip module may include stacking multiple die in a package. Two of the common die stacking methods are: (a) larger lower die combined with a smaller upper die, and (b) so-called same-size die stacking. With the former, the die can be very close vertically because the electrical bond pads on the perimeter of the lower die extend beyond the edges of the smaller die on top. With same-size die stacking, the upper and lower die are spaced more vertically apart to provide sufficient clearance for the wire bonds to the lower die. As discussed, both these methods have inherent KGD and assembly process yield loss disadvantages since KGD cannot be used for fabricating these configurations.
Another previous design is package level stacking or package on package (POP). This concept includes stacking of two or more packages. KGD and assembly process yields are not an issue since each package can be tested prior to assembly, allowing KGD to be used in assembling the stack. But package level stacking can pose other problems. One problem is package-to-package assembly process difficulties caused by irregularities in the flatness/coplanarity of the lower package. Another problem results from the increased stiffness of the overall assembly, which can lead to reduced board level reliability. Still another problem can arise from poor heat dissipation from the upper package. Thus, despite the advantages of recent developments in semiconductor fabrication and packaging techniques, there is a continuing need for improved packaging methods, systems, and designs for increasing semiconductor die density in PCB assemblies.
Thus, a need still remains for an efficient 3D package stacking process. In view of the ever-increasing need to save costs and improve efficiencies, it is more and more critical that answers be found to these problems. Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.